The invention relates generally to ignition systems such as can be used, for example, with gas turbine engines. More particularly, the invention relates to an exciter circuit for and ignition system with the use of an output step-up transformer in the discharge circuit of the exciter.
Conventional ignition systems typically include one or more igniters through which energy is discharged from an energy storage device such as a capacitor. The discharge is characterized by a high energy spark or plasma discharge that occurs following a high voltage ionization or breakdown across the igniter gap, including air gap and semiconductor gap igniter plugs.
A conventional ignition system for an internal combustion engine, such as, for example, a gas turbine aircraft engine, includes a charging circuit, a storage capacitor, a switching circuit, a discharge circuit and at least one igniter plug located in the combustion chamber. The switching circuit may include one or more switching devices connected in series between the capacitor and the discharge circuit and plug.
In a high voltage exciter circuit, such as is typically associated with the use of air gap and semiconductor igniter plugs, it is generally known to use a step-up transformer as part of the discharge circuit. A typical system is illustrated in U.S. Pat. No. 5,510,952 issued to Bonavia et al. In some applications, however, it is desired to minimize or eliminate the presence of the step-up transformer impedance in the discharge circuit after the spark discharge is initiated. One such attempt is illustrated in U.S. Pat. No. 5,084,800 issued to Hijikata. This effort falls short, however, of eliminating the transformer impedance from the discharge circuit during the spark discharge interval.
The objectives exist, therefore, for an exciter discharge circuit that provides a high voltage for an igniter plug but which exhibits no transformer impedance during the spark discharge period.